The present invention relates to a method for replacing stay cables that support a bridge deck to a main tower, and a temporary hanger for use in this method to replace stay cables.
For example, a cable-stayed bridge is known as a bridge with a bridge deck supported to a main tower by stay cables.
FIG. 16A illustrates a structure of a typical cable-stayed bridge. FIG. 16A illustrates that a cable-stayed bridge 101 includes a main tower 102, a bridge deck 103, and a plurality of stay cables 104. The main tower 102 is disposed vertically. The bridge deck 103 is disposed horizontally and crosses the main tower 102. The plurality of stay cables 104 are hung in tension and sloped with respect to the main tower 102 and the bridge deck 103. This structure allows the bridge deck 103 to be supported to the main tower 102 through the stay cables 104.
FIG. 16B illustrates that the stay cable is being hung on the cable-stayed bridge in FIG. 16A (see, e.g., Japanese Unexamined Patent Publication No. H7-331615). FIG. 16B illustrates that a hanging tool 112 of a tower crane 111 is holding a vicinity of one end, of the stay cable 104, which is being fixed to main tower 102. A hanging tool 114 of a mobile crane 113 is holding a vicinity of the other end, of the stay cable 104, which is being moved to a predetermined position opposite to the main tower 102 and being fixed to the bridge deck 103.
FIG. 17A illustrates a structure of a fixing portion, of the stay cable, which is on the bridge deck side. FIG. 17A illustrates that the stay cable 104 is disposed inside an anchor pipe 121 through an upper opening thereof. The anchor pipe 121 is tilted and fixed at a predetermined angle with respect to the bridge deck (not shown). A socket 104a on the bridge deck side is disposed on a tip end of the stay cable 104, and appears from a lower opening of the anchor pipe 121. A bearing plate 122 and a shim plate 123 fix the stay cable 104 in the vicinity of the lower opening of the anchor pipe 121.
FIG. 17B illustrates that the stay cable is being pulled into the fixing portion on the bridge deck side in FIG. 17A. FIG. 17B illustrates that, to pull the stay cable 104, a jack 142 and a strand base 143 are installed on the lower opening of the anchor pipe 121 through a jack base 141. A tension rod 131 is mounted on the socket 104a on the bridge deck side of the stay cable 104. A PC strand 132 is mounted opposite to the socket 104a on the bridge deck side with respect to the tension rod 131. Then, the PC strand 132 is inserted into the anchor pipe 121 to be acted upon by the jack 142, and allows the tension rod 131 to be pulled into the anchor pipe 121. After this primary pulling by the PC strand 132, the strand base 143 is detached for the tension rod 131 to be acted upon by the jack 142, and the stay cable 104 is pulled into the anchor pipe 121. This secondary pulling is conducted by the tension rod 131 until the socket 104a on the bridge deck side of stay cable 104 appears from the lower opening of the anchor pipe 121. Then, as illustrated in FIG. 17A, the stay cable 104 is fixed with the bearing plate 122 and the shim plate 123.